Your score is not too bad, 6min22.1 without cw translates into ~6min19.0 with CW, which is about on par with other Samsung scores in this thread. Note that all the top Samsung times are done in 4x4Gb configs, which is said to be at least 1 second faster.

If you're on air, then it's a lot easier to get a good time (sub 6min20) with Samsungs than PSC. You don't need to have super duper PSC kits to do 1300+ CL6 / CL7-tWCL7 on LN2, properly tweaked average stuff should be able to do it too.
BTW, you can no longer find good Samsungs in retail as well

Here's something I've been working on last week. Also no CW and timings not minimised as the board started acting funny after this run.